Summary: IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 21, NO. 3, JUNE 2011 2615
Nonlinear Near-Field Microwave Microscope for RF
Defect Localization in Superconductors
Tamin Tai, X. X. Xi, C. G. Zhuang, Dragos I. Mircea, and Steven M. Anlage
Abstract--Niobium-based Superconducting Radio Frequency
(SRF) cavity performance is sensitive to localized defects that
give rise to quenches at high accelerating gradients. In order
to identify these material defects on bulk Nb surfaces at their
operating frequency and temperature, it is important to develop a
new kind of wide bandwidth microwave microscopy with localized
and strong RF magnetic fields. By taking advantage of write head
technology widely used in the magnetic recording industry, one
can obtain 200 mT RF magnetic fields, which is on the order
of the thermodynamic critical field of Nb, on sub-micron length
scales on the surface of the superconductor. We have successfully
induced the nonlinear Meissner effect via this magnetic write
head probe on a variety of superconductors. This design should
have a high spatial resolution and is a promising candidate to find
localized defects on bulk Nb surfaces and thin film coatings of
interest for accelerator applications.